1. Field of the Invention
This invention relates to a method of and an apparatus for machining a workpiece with plural tool heads, more particularly, to a method of and an apparatus for in-process machining simultaneously plural portions of one workpiece with plural tool heads each of which have a tool.
2. Description of the Related Art
As disclosed in Japanese Laid-Open Patent Application No. S54(1979)-71495, it is known such a grinding machine which grinds two pin portions of one crankshaft eccentrically moving around its journal portion as rotational center, in which two wheel heads are independently advanced and retracted synchronously with a rotation of a main spindle.
Meanwhile, International Patent Publication (PCT) WO97/12724 discloses an in-process gauging apparatus. This gauging apparatus can measure a diameter of a pin portion that is moving eccentrically during grinding process.
Generally, a cylindrical grinding is executed by three processes that are rough grinding process, finish grinding process and spark-out process in this order. In the finish grinding process, a diameter of a pin portion is measured by such as above described in-process gauge. When the measured diameter of the pin portion became a required value, feed motion of a wheel head is stopped and rotation of a main spindle is kept. The spark-out process is executed to keep the wheel head in its stopped position during predetermined time or predetermined number of a workpiece rotation. The grinding in the spark-out process removes deflection of the workpiece that is occurred during rough grinding process of finish grinding process. Therefore, it improves accuracy of radial dimension and roundness of the grinding portion.
As to a grinding machine that has two wheel heads, motion of each wheel head is controlled independently. Because two diameters of grinding portions before grinding are different and conditions of two grinding wheels are different, grinding processes by two wheel heads are not progress in same condition. Namely it happens that when the diameter of the portion which is ground by one grinding wheel become a required value and the spark-out process is started, it can be happened a diameter of another portion which is ground by another grinding wheel has not become a required value. In the spark-out process by one grinding wheel, a workpiece is deflected by a grinding force occurred by another grinding wheel which is still executing finish grinding process. Therefore, accuracy of diameter and roundness of the portion ground by one grinding wheel is deteriorated by effect of the grinding by another grinding wheel.
Accordingly, an object of the present invention is to solve the above mentioned problems and is to provide a machining method of and apparatus for simultaneously machining at least two machining portions of a workpiece with plural tool heads, in which a deterioration is prevented in machining an accuracy of a diameter and roundness of one machined portion by effect of another machining portion.
Another object of the present invention is to provide a machining method of and apparatus for simultaneously machining at least two machining portions of a workpiece with plural tool heads, which enables to perform machining in short cycle-time.
In order to achieve the above objects, the present invention provides an improved machining method of simultaneously machining at least two machining portions of a workpiece with plural tool heads. The machining method comprising: executing a first machining process for the machining portions under measuring each diameter of the machining portions; backing off one tool head predetermined distance, one tool head corresponds one machining portion whose diameter became a required value during the first machining process; and executing a second machining process for the machining portions after diameters of all of the machining portions became each required value.
Since one tool head corresponding to one machining portion whose diameter became a required value first is backed off and a tool of one wheel head is disengaged the machining portion, the tool of one wheel head does not effect any influence to machining for another machining portions. Therefore, machining force acted to workpiece by each tool is not imbalanced, so that it can achieve high accuracy machining without lengthening a machining cycle-time.
In order to achieve the above objects, the present invention provides an improved machining apparatus for simultaneously machining at least two machining portions of a workpiece with plural tool heads. The machining apparatus comprising: a base; a worktable until arranged on the base, which rotatably support the workpiece around predetermined axis; at least two tool heads movably arranged on the basis in a direction to cross the rotational axis of the workpiece, each of the tool heads supports a tool; feeding units corresponding to the tool heads, the feeding units move each of the tool heads; gauging units arranged corresponding to each of the machining portions, said gauging units measure each diameter of the machining portions at least during a first machining process; and a control unit controlling the feeding units according to signals of diameters provided from each of the gauging units. Further, the control units controls all of the feeding units to execute a first machining process; controls one feeding unit to back off one tool head predetermined distance, one tool head corresponds one machining portion whose diameter became a required value during the first machining process; and controls all of the feeding units to execute a second machining process for the machining portions after diameters of all of the machining portions became each required value.
Since one tool head corresponding to one machining portion whose diameter became a required value first is backed off and a tool of one wheel head is disengaged the machining portion, the tool of one wheel head dose not effect any influence to machining for another machining portions. Therefore, machining force acted to workpiece by each tool is not imbalanced, so that it can achieve high accuracy machining without lengthening a machining cycle-time.